The involvement of the tumor suppressor protein p53 in the process of tumorgenesis is well established. However, little is known about the function and regulation of p53 at the molecular level. It is known that p53 can be phosphorylated in vitro by cell cycle dependent kinases and casein kinase II, but the function and the regulation of such processes is still not clear. The goals of our project are to examine the roles of phosphorylation on p53's function as a tumor suppressor protein, to elucidate possible regulatory mechanisms of p53 phosphorylation, and to examine the involvement of nutritional and/or hormonal factors that may serve as effectors of this process. We have taken a molecular biological approach, which utilized manipulation of cDNA coding for the p53 by site- directed mutagenesis, to alter specific amino acid residues that are suspected phosphorylation sites. This approach will allow us to examine effects of specific changes in the protein. At present, we are in the process of developing a cell culture system which will allow us to assess the effects of the changes.